I used to harvest parts, but the first step I used before harvesting, Was knowing what they were used for. Knowing the part numbers was essential. Knowing if the parts specifications made it usable for what I was doing told me if it was worth the effort or not. And I only harvested certain types of components. Transistors, Socketed integrated circuits and transformers. Maybe a rectifier or special capacitor or resistor, But only if there was something really special about them. That was in the 70s and 80s. But many of these components were not readily available. Nowadays with the Internet, everything is available. It would cost you more to harvest some of these components than it would to just buy them out right. Only harvest special components that are very expensive or hard to get. And only if you know what the component is, And have the Datasheet.